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Title: Characterising room temperature ionic liquids with acoustic wave devices
Author: Doy, Nicola
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2010
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Data for the physical properties of Room Temperature Ionic Liquids (RTILs) as a function of chemical composition is limited due to the expense and difficulty of producing large volumes of pure samples for characterization. RTILs comprise solely of ions and are liquid at room temperature. These are becoming of increasing interest for an extensive range of applications. This thesis looks at developing small scale characterization processes to find low cost and efficient methods for processing smaller sample volumes. Quartz crystal impedance analysis has been used to assess whether room temperature ionic liquids behave in a Newtonian manner to determine the values of their square root viscosity-density product using small volumes. Values are compared to traditional viscometer and densitometer measurements. A range of harmonics were studied for a 5 MHz fundamental crystal. The frequency shift of the third harmonic was found to provide the closest agreement between the two measurement methods with a limit seen at a square root viscosity-density product value of approximately 18 kg m⁻² s⁻⁰.⁵. Further characterisation of the liquid was performed to separate values of density and viscosity using dual Quartz Crystal Microbalance (QCM) with fabricated surface features on one QCM; this required a total sample volume of only 240 L. Values were corroborated with standard measurement techniques demonstrating good agreement. A QCM was then incorporated into a microfluidic glass chip system to measure the square root of the viscosity-density product of RTILs. The QCM covers a central recess on the glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of an 8 MHz QCM operating on the 3rd harmonic was shown to allow determination of the square root viscosity-density product of RTILs to a maximum limit of square root viscosity-density product of approximately 10 kg m⁻² s⁻⁰.⁵. This microfluidic technique reduced the sample size needed for characterisation from 1.5 ml to only 30 μL and allowed the measurement to be made in an enclosed system reducing the risk of water contamination. In the final part of this work surface acoustic wave devices were studied. The most promising device, a Shear Horizontal Surface Acoustic Wave (SH-SAW) device with silicon dioxide guiding layer, provided good correlation between phase, insertion loss and the square root viscosity-density product. A maximum square root viscosity-density product limit was observed at approximately 10 kg m⁻² s⁻⁰.⁵ at which point the acoustic response becomes too damped for accurate results to be determined. This work provides a basis for further miniaturisation and characterisation which could develop a surface acoustic wave device based system for high throughput microfluidic characterisation of many properties of ionic liquids within a single chip.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available